(a) Technical Field
The present invention relates to a coolant demineralizer for a fuel cell. More particularly, it relates to a large-area demineralizer, which removes ions from coolant within a fuel cell.
(b) Background Art
A fuel cell system employed in a hydrogen fuel cell vehicle of an environment-friendly vehicle typically includes a fuel cell stack for generating electricity by an electrochemical reaction of reactant gases, a hydrogen supply system for suitably supplying hydrogen as a fuel to the fuel cell stack, an air supply system for suitably supplying oxygen-containing air as an oxidant which is required for the electrochemical reaction in the fuel cell stack, a thermal management system for suitably removing reaction heat from the fuel cell stack to the outside of the fuel cell system, controlling operation temperature of the fuel cell stack, and performing a water management function, and a system controller for controlling the overall operation of the fuel cell system.
In the above configuration, the fuel cell stack suitably generates electrical energy via the electrochemical reaction of hydrogen and oxygen as reactant gases and discharges heat and water as by-products of the reaction. Accordingly, a system for cooling the fuel cell system in order to prevent the temperature rising within the fuel cell stack is required.
In a typical fuel cell system for a vehicle, a water cooling system for circulating water through a coolant channel in the fuel cell stack is used to cool the fuel cell stack, thus maintaining the fuel cell stack at an optimal temperature as a result.
An exemplary configuration of the cooling system of the fuel cell vehicle is shown in FIG. 1. FIG. 1 is a schematic diagram of a coolant loop of the fuel cell vehicle, which includes a coolant line 3 disposed between a fuel cell stack 1 and a radiator 2 to circulate coolant, a bypass line 4 and a three-way valve 5 for bypassing the coolant so the coolant is not passed through the radiator 2, and a pump 6 for pumping the coolant through the coolant loop.
The applicable materials for pipes/tubes/connection lines through which the coolant is fluidly communicated, which constitute the coolant loop of the fuel cell system, is very limited due to the amount of ions that are often released into the coolant by various materials. Thus, the materials chosen should have a low ionic release rate.
When cheap materials are used, impurities and ions are released from the material, which is in contact with the coolant. As a result, the electricity generated from the fuel cell stack could flow through the coolant, which can be problematic. Further, when the ion conductivity of the coolant is increased by materials used in the fuel cell vehicle, which moves while generating electricity and carrying a driver and passengers, electricity may flow through the coolant loop, which may make it very difficult for electrical devices and driving components, mounted in the vehicle, to normally operate and further may cause serious danger (such as an electric shock) to the driver and passengers. As a result, the electrical conductivity of the coolant in the fuel cell vehicle needs to be measured at all times, and a control logic for shutting down the fuel cell system when the electrical conductivity is increased to or beyond a predetermined level is employed.
Moreover, a demineralizer 7 is provided in the coolant loop to maintain the ion conductivity of the coolant below a predetermined level. The demineralizer 7 serves to reduce the ion conductivity below a predetermined level by filtering ions contained in the coolant flowing through the fuel cell stack 1.
FIG. 2 is a perspective view of a conventional demineralizer, FIG. 3 is a longitudinal cross-sectional view of FIG. 2, and FIG. 4 is a diagram showing a differential pressure region (in which an ion resin is filled) in the conventional demineralizer.
The demineralizer 100 typically includes a housing 110 through which coolant is passed, an inlet port 120 and an outlet port 130 through which the coolant is introduced and discharged, an ion resin 101 filled in the housing 110 to filter ions contained in the coolant, and mesh assemblies 140a and 140b for supporting the ion resin 101 filled in the housing 110 to prevent the ion resin 101 from leaking.
In the above configuration, the mesh assemblies 140a and 140b serve to suitably pass the coolant through the housing and entrap the ion resin 101 in the form of small grains in the housing 110. The mesh assemblies 140a and 140b are suitably provided at both the inlet port 120 and the outlet port 130 at both ends of the housing 110 to prevent the ion resin 101 within the housing 110 from leaking.
In the demineralizer 100 having the above-described configuration, the coolant introduced through the inlet port 120 of the housing 110 passes through the mesh assembly 140a, the ion resin 101, and the mesh assembly 140b and is then discharged through the outlet port 130 of the housing 110. While the coolant passes through the ion resin 101, ions are filtered and removed. The removal of ions from the coolant makes it possible to suitably prevent current leakage from the fuel cell stack, and thereby improves the electrical safety of the vehicle to meet industrial standards.
However, in the conventional demineralizer 100 shown in FIGS. 2 to 4, the coolant flows through a longitudinal/vertical path between the inlet port 120 and the outlet port 130, and the region, in which the ion resin 101 is filled, along the longitudinal path corresponds to a region in which a difference in coolant pressure (differential pressure) occurs between the inlet side and the outlet side. As a result, the coolant passing through the region in the longitudinal (axial) direction increases the differential pressure region in the demineralizer 100 (the region in the longitudinal direction in which the ion resin is filled in FIGS. 3 and 4, i.e., the region between the top and bottom of the housing), and thus a considerable difference in pressure occurs between the coolant introduced through the inlet port 120 and the coolant discharged through the outlet port 130.
FIG. 5 is a graph showing an increase in differential pressure with respect to an increase in coolant flow rate in the conventional demineralizer. As can be seen from FIG. 5 there is a large differential pressure, which forms when the flow rate of coolant is increased.
It is known that when the coolant passes through an ion resin layer in the longitudinal direction, the region of the ion resin layer, where the coolant introduced through the inlet port is filtered, that is, the width or area of the ion resin layer, which actually removes ions, within the coolant flow path in the longitudinal direction, is about typically about 15 to 30 mm The ion resin in the downstream section beyond this width of the ion resin layer, which actually removes ions, typically has a lower filtering effect, and thus it is not necessary to increase the length of the ion resin layer to or beyond the longitudinal length of the housing. The ion resin in the downstream other than the region, which contributes to the actual filtering, is unnecessary.
Accordingly, when the demineralizer is configured so that the coolant is suitably introduced through one end of the housing, passes through the ion resin layer in the longitudinal direction, and reaches the other end of the housing, an excessive amount of the ion resin is used, which increases the manufacturing cost and significantly increases the differential pressure in the system.
Further, while the ion resin layer in the vicinity of the outlet port, through which the coolant is suitably discharged, is not used for the filtering of ions, the ion resin layer in the vicinity of the inlet port, through which the coolant is suitably introduced, is mainly used for the filtering of ions. Therefore, when the demineralizer must be replaced with new one due to a long-term use of the ion resin in the vicinity of the inlet port, it is necessary to replace the entire demineralizer with new one, although the ion resin in the vicinity of the outlet port is still usable, while the ion resin in the vicinity of the inlet port is not. This inefficient use of materials leads to increased maintenance costs.
Further, as shown in FIG. 1, the conventional demineralizer is mounted in a bypass loop, rather than in a main coolant loop. In the demineralizer as shown in FIGS. 2 to 4, a high differential pressure is formed due to the increased length of the differential pressure region in the ion resin layer and, as a result, it is very difficult to effectively circulate the coolant. Problematically, because the coolant does not flow smoothly through the system, there is a significant reduction in the ionic filtering effect, and thereby the electrical conductivity is not sufficiently reduced during initial start-up of the vehicle. As a result, it is difficult to prevent the current leakage during the initial start up of the vehicle.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.